July 2004

The abandoned Runehamar road tunnel on the southwest coast of Norway has been redesigned and given new life as a site for the experimental burning of trucks, cargo, and other vehicular structures in order to learn how subterranean road fires can best be extinguished.

It's a kind of Nordic funeral pyre built not for the bodies of kings but for the products of the automotive industry, an underground bonfire of simulated car wrecks that seems more like something you'd see in the fiction of J.G. Ballard.

The overall structure has been modified to serve as a closely-controlled thermal environment—more a furnace than a piece of transportation infrastructure—complete with an array of instruments and sensors, and a system of sprinklers and ventilation fans that let observers try out novel methods of fire suppression.

In a sense, this is what might happen if someone like architect Philippe Rahm was given a limited budget and hired to design experimental subterranean road infrastructure, with his work's focus on the thermal behavior of spaces and other non-visual dimensions of the built environment.

There is a need for more detailed knowledge on how and why various semi-trailer cargos burn so strongly and why they spread so quickly. The high heat exposure from the semi-trailers to the tunnel linings also needs more focus. The only reasonable way of finding an answer to these questions is to carry out systematic large scale experiments that can provide a better basis for the design of technical systems in road tunnels.

There's more to write about the tunnel, I'm sure, and there is a bit more detail in the original post on Gizmodo—including, for those of you curious, this PDF that comes complete with structural and thermal diagrams of the burning apparatus.

But I suppose I'm more interested in the sheer strangeness of an old road tunnel being transformed into a venue for controlled thermal events. It is ritualistic, repetitive, and pyromaniacal, as if vitamin-D-deprived engineers in lab coats have been endlessly sacrificing sacred cargo for some infernal mountain, an altar for automotive transubstantiation, where unknown driving objects are reduced to ash and studied, again and again, filmed and re-watched—until the next fire, when the sprinklers fill up again and the vents, like a buried engine, begin to roar.

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I've done a lot of testing of rocket vehicles, and for some projects it involved hovering over a concrete pad for minutes at a time, as in https://www.youtube.com/watch?v=Rn6xIfY_3zM

The rocket plume is not just a fuel air fire, but a fuel/liquid oxygen fire, so it's even hotter. At short distances, it can cut through concrete at a rate of an inch in less than a minute.

Though some of the concrete melts, the cause of the fastest regression is water bound in the concrete boiling and spalling off chunks of concrete, which go flying through the air as concrete shrapnel.

What's the relevance to this story? It turns out that it' basically the same problem faced by engineers trying to make concrete tunnels that won't collapse in a fire. They found that adding plastic fibers to the concrete will give a route for the steam to escape after the fire melts the plastic. By letting the steam out, the concrete stays intact for much longer in a fire.

The end result is that at my last company we had an unusual concrete pad made with a tunnel mix of concrete, so that it'd last longer when we shoot hypersonic gas at it.

somehow i'm not surprised that this is happening in Norway. I remember my first visit there, at the summer solstice, when i was witness to the entire population taking to the beaches to light giant bonfires & cavort before them. It all felt a bit too 'Wicker Man'…

All of my resources are googlable, the terms spalling concrete fire fibers find them. The "An Experimental Study on Spalling of High Strength Concrete..." paper includes the funny-to-me idea of not just one, but two different standard fires, ISO834 and DIN4102-11.

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BLDGBLOG ("building blog") is written by Geoff Manaugh. The opinions expressed here are my own; they do not reflect the views of my friends, editors, employers, publishers, or colleagues, with whom this blog is not affiliated.